(1) Field of the Invention
The present invention relates to a method and apparatus for a gamma compensation of a color camera.
(2) Description of the Related Art
In a color television apparatus, the level of an input frequency and the level of output light-emission of a cathode ray tube have a nonlinear relationship (gamma characteristic of the cathode ray tube). Therefore, a so-called gamma compensation or reverse-compensation for the gamma characteristic of the cathode ray tube is performed on the camera side, thereby providing an easy-to-see image.
The gamma compensation is carried out by changing the gain of an amplifier in accordance with the level of the input signal.
There is a conventional basic gamma compensator which acquires the input/output characteristic as an approximation of an inclination-changing line.
The conventional gamma compensator however has the following shortcomings.
First, the frequency responses for the operating portions corresponding to individual line segments which constitute the input/output characteristic cannot be determined independently. For instance, if one tries to perform adjustment to provide the best frequency response in a black level region where the signal level is low, the adjustment will affect the frequency response in a region where the signal level is high. Therefore this necessitates setting the frequency response in light of a balance over the whole level range, making it difficult to provide the optimal frequency response for each level range.
Secondary, it is necessary to take a wide dynamic range because an approximation is acquired by adding signals.